In the new generation of wireless communication access technologies, a User Equipment (UE for short) accesses to an Evolved Packet System (EPS for short) through an Evolved Universal Terrestrial Radio Access Network (E-UTRAN for short) base station system, and can obtain permanent online Internet Protocol (IP) service capabilities. When the UE is attached to the network, the network allocates an IP address which is continuously unchanged in an attach period to the UE. At any time in the attach period, a data request transmitted by an Application Server (AS for short) may directly use the IP to transmit downlink IP data to the UE.
FIG. 1 is a diagram of architecture of an EPS packet network to which a UE accesses through an E-UTRAN base station system, wherein the EPS packet network is comprised of a base station system and a core network system. The primary network elements of the base station system, i.e., an E-UTRAN base station system, are Evolved NodeBs (eNB for short). The core network system primarily comprises a Mobility Management Entity (MME for short), a Serving Gateway (S-GW or SGW for short), a Packet Data Network Gateway (PDN GW or P-GW or PGW for short), and a Home Subscriber Server (HSS for short). Wherein, the MME is responsible for allocating and managing user plane resources, and mapping the user plane resources to air interface resources on the eNodeB and user plane bearers on the SGW/PGW. When the UE is in an inactive state for a long time, the eNodeB will initiate a radio resource release process, i.e., releasing radio air interface bearer resources allocated to the terminal and user plane bearer resources on the S1 interface between the eNodeB and the SGW, and then the UE enters an IDLE state. When the UE wants to transmit data in an IDLE state, the eNodeB needs to interact with the MME to recover bearer resources allocated to the UE, including air interface bearer resources on the eNodeB and user plane bearer resources of the S1 interface between the eNodeB and the SGW.
FIG. 2 illustrates a bearer resource recovery process when the UE is attached to the network and then wants to initiate uplink data transfer in an IDLE state (i.e., Radio Resource Control-IDLE (RRC-IDLE)). When the UE wants to transmit data to a remote end (for example, application server) in an IDLE state, the UE must firstly set up an RRC connection to recover to a connected state. The process includes steps S201-209.
In step S201, the UE transmits an RRC Connection Request message to the eNodeB, which carries identity information of the UE, wherein, an S-Temporary Mobile Subscriber Identity (S-TMSI for short) is used here.
In an IDLE state, the UE initiates an RRC Connection Request message using a number #0 Signaling Radio Bearer (SRB for short), i.e., SRB0. The SRB0 is a shared signaling radio bearer resource, and the designed message capability per UE is very small, and is generally only used for initiating an initial RRC message and carries most necessary information elements (such as, UE identity (ID)), wherein, the ID provided by the UE is the S-TMSI here.
In step S202, after receiving the RRC connection request message, the eNodeB transmits an RRC Connection Setup message to the UE.
The message is used to indicate the UE to set up a number #1 signaling radio bearer, i.e., SRB1, which is allocated to each user, and may carry Non-Access Stratum (NAS) signaling with a certain length. After the SRB1 is allocated, the UE may initiate the NAS message using the SRB1.
In step S203, the UE transmits an RRC Connection Setup Complete message to the eNodeB. In the message, the UE carries an NAS message to be transmitted. The NAS message carried by the UE is a Service Request (SR for short) message here.
In the step, the UE transmits the NAS message using the SRB1. The SRB1 per se has certain capability limitation, and cannot be used to transmit a large NAS message. In subsequent steps, the eNodeB will indicate the UE to set up a number #2 signaling radio bearer, i.e., SRB2, and a Data Radio Bearer (DRB for short). The two radio bearers may carry an NAS message with a large capacity. The DRB is generally used to transmit IP data streams.
In step S204, after receiving an RRC connection setup complete message of the UE, the eNodeB acquires the NAS message therefrom, encapsulates the NAS message in an Initial UE Transfer message of the S1 interface, and transmits the message to the MME. All NAS messages transmitted by the UE are transparently transmitted to the MME by the eNodeB.
In step S205, after receiving the Service Request message transmitted by the UE, the MME enables the UE to enter a connected state (i.e., EPS Mobility Management-CONNECTED (EMM-CONNECTED)). At the same time, the MME transmits an Initial Context Request message to the eNodeB, which comprises a security key of the UE, EPS bearer context information, an SGW address allocated to the UE, and a radio capability of the UE etc.
In step S206, the eNodeB initiates a Security Mode Setup message to the UE, to require the UE to transmit subsequent signaling and data using an encryption method.
After the eNodeB receives the Initial UE Context Request message transmitted by the MME in step S205, the eNodeB initiates a security mode setup request to the UE using the security key in the message.
In step S207, the UE replies to the eNodeB with a Security Mode Setup Complete message, which represents that the security mode request has been received, and the security mode has been set up. Thereafter, the encryption mode is used to transmit signaling and data between the UE and the network.
In step S208, the eNodeB transmits an RRC Connection Reconfiguration Request message to the UE, which carries Radio Access Bearer (RAB for short) information.
With the RAB information, the eNodeB requires the UE to set up the indicated radio bearers, which comprise the SRB2 and a number of DRBs. These DRBs correspond to the bearers of the core network of the UE one by one.
In step S209, the UE transmits an RRC Connection Reconfiguration Complete message to the eNodeB, which indicates that the radio bearer has been configured completely.
After step S209 is performed, the UE may initiate an NAS message with a large capacity using the SRB2; and may further transmit an uplink IP data stream, the eNodeB transmits the IP data stream to the SGW corresponding to the UE, and the SGW transmits the IP data stream to the PGW.
In step S210, after receiving the RRC connection reconfiguration complete message transmitted by the UE, the eNodeB returns an Initial Context Configuration Response message to the MME.
In step S211, after receiving the Initial Context Configuration Response message transmitted by the eNodeB, the MME transmits a Modify Bearer Request message to the SGW/PGW.
In the step, the MME notifies the SGW/PGW according to the reception condition of the bearer by the UE/eNodeB to modify the bearer. The message enables the SGW to recover the bearer resources of the S1-U with the eNodeB at the same time.
In step S212, the SGW/PGW returns a Modify Bearer Response message to the MME.
After step S212, the SGW may receive the uplink IP data packet transmitted by the UE, and forwards it to the PGW.
In step S213, after the eNodeB receives the RRC request of the UE, the eNodeB sets a de-activation timer for the UE, and after the timer expires, if the UE is no longer active, a resource release process is triggered.
In step S214, if the de-activation timer of the UE on the eNodeB expires and the UE is inactive, the eNodeB initiates a UE Context Release Request message on the S1 interface to the MME.
In step S215, after receiving the UE Context Release Request message initiated by the eNodeB, the MME transmits a Release Access Bearer Request message to the SGW.
In step S216, after releasing the bearer of the S1-U interface with the eNodeB, the SGW returns a Release Access Bearer Response message to the MME.
In step S217, the MME transmits a UE Context Release Command message to the eNodeB.
In step S218, after receiving the UE Context Release Command message of the MME, if the UE is currently inaccessible, the eNodeB transmits an RRC Connection Release message to the UE, and on the other hand, the eNodeB releases the UE context information.
In step S219, the eNodeB returns a UE Context Release Complete message to the MME.
After steps S214-S219, after the UE is inactive, the eNodeB will release the radio bearers of the UE, the UE context, and the bearer context of the S1-U interface, the MME will release the UE context and enables the UE to enter an IDLE state, and the SGW will release the bearer context of the S1-U interface.
As shown in FIG. 2, in the flow of the UE entering a connected state from an IDLE state, recovering bearer resources, initiating data transfer, and finally entering an IDLE state, in order to enable the IP data to be transmitted to the SGW, the eNodeB needs to firstly find the SGW and recover the data transfer tunnel with the SGW, which needs interaction between the eNodeB and the MME and needs to obtain the bearer related information of the SGW and the S1 interface from the MME. In a case that a large number of terminals frequently initiate a small amount data transfer and rapidly enter an IDLE state after transmitting the small amount data transfer, the existing flow easily results in too much load of the network signaling, and easily results in congestion of the control network elements. On the other hand, the data traffic transmitted by these terminals is much less than the signaling traffic resulting from these terminals entering the connected state from the idle state, which results in extremely low efficiency of the system.